The objective of this research project is to clarify the relationship between membrane function in epithelia and membrane structure as revealed by freeze-fracture electron microscopy. In particular, the functional significance of vasopressin-induced intramembranous particle aggregates found in membranes of the toad bladder will be studied by correlation of their frequency with specific functional changes and by utilizing the deep-etching technique. Assessment will also be made of the extent to which similar vasopressin-induced membrane structural changes exist in other epithelia known to respond to vasopressin. The effect of aldosterone on membrane structure and vasopressin-induced structural alterations will also be examined. In addition, studies are planned of the structure of the zonula occludens in unfixed epithelia frozen in physiological solutions and an investigation of the effect of glutaraldehyde fixation on the permeability of the junction in isolated renal proximal tubules.